There has been no great acceleration toward the finish line in the journey to reinstitute supersonic civil air travel. The process of revisiting the halcyon days of Concorde—which last flew in 2003—has been slow and, at times, controversial. The hurdles are not only technical but perhaps, more significantly, economic, political, and social.

A 13-page working paper released yesterday by the International Council on Clean Transportation (ICCT) casts a shadow on optimism for successfully reintroducing supersonic flight, though it leaves smaller supersonic business jets—such as Aerion’s in-development, Mach 1.4 AS2—out of its line of fire.

This week at the Farnborough Airshow, Boom Aerospace told AIN it now expects to fly its GE J85-15-powered “Baby Boom” demonstrator sometime next year, a precursor to its planned 55-seat, Mach 2.2 Boom airliner. As of January, the plan had been to get the demo ship airborne this year. It is now under assembly near Denver, Colorado, with flight tests slated for California.

Boom founder and CEO Blake Scholl told AIN here at the show that engines and hydraulic systems have been powered up, and the development team has tested the wing spar, composite joints, and completed low-temperature trials. A second, separate engineering team is working on the final product.

Scholl reports the company is funded through first flight and has already raised $85 million, including $10 million from launch customer Japan Airlines. In December, JAL placed an order for 20 at a price of $200 million each.

Scholl answered the question of where the Boom would be produced—in the U.S. He also projects fares for supersonic flights on the Boom to be on par “with subsonic business class.” He projected costs per seat mile to be in that range, adding, “We want to get the cost of speed down.” Entry into service has also stretched out, previously projected as early as 2023 but now set for 2025.

For its part, ICCT projects that the best-case per-passenger fuel burn for a supersonic airliner would be three times that of a business-class traveler on a current subsonic airliner. That jumps to nine times as much fuel for an economy-class passenger flying in a supersonic airliner at subsonic speeds, which would be required over territorial North America.

The paper suggests that supersonic airliner proponents have two pathways to success—either develop aircraft based on new, clean-sheet engines or lobby international policymakers to establish separate standards and environmental rules for supersonic airline travel. For example, ICCT suggested that using area-rule aerodynamics would reduce wave drag and increase efficiency. The paper also notes, “The engine model used in this work is a low-fidelity model. Engine and component efficiency is based on technology level estimates from…2006.”

In the category of going still faster—albeit much further into the future—Boeing is here with its concept of a hypersonic airliner, a class generally thought to be capable of speeds up to Mach 10. While details are few, Boeing said it could fly such an aircraft in 20 to 30 years.